simplification in fully optimized code. It occurs sporadically in the testsuite, and
many times in 403.gcc: the final bitcode has 131 fewer subtractions after this change.
The reason that the multiplies are not eliminated is the same reason that instcombine
did not catch this: they are used by other instructions (instcombine catches this with
a more general transform which in general is only profitable if the operands have only
one use).
llvm-svn: 123754
the original instruction, half the cases were missed (making it not
wrong but suboptimal). Also correct a typo (A <-> B) in the second
chunk.
llvm-svn: 122414
Duncan Sands